Whether whale or moth, animals that swim or fly use universal rules

A diverse array of animals, including fish, birds and insects, have similar wing-bending properties, according to a paper in Nature Communications.

A diverse array of animals, including fish, birds and insects, have similar wing-bending properties, according to a paper in Nature Communications. (F. Jaine)

Amina Khan

If birds of a feather flock together, get ready to make some room. It turns out that across the animal kingdom, winged and finned creatures -- from tiny insects to giant whales – share some incredible energy-saving features in their body designs. The findings, published in Nature Communications, could give engineers important principles they can use to create stronger, more efficient swimming and flying robots.

Researchers have long had trouble trying to develop robots that can move as efficiently as animals can, said study coauthor John Costello, a biologist at Providence College in Rhode Island. And part of the problem is that robots typically involve very rigid bodies, which is very unlike the flexible forms of many flying and swimming creatures. But while building a jellyfish robot with a hard shell, Costello and colleagues found that if they added a silicone flap around the robo-jelly, it made the swimming bot on the order of a thousand times more efficient.

Clearly, a flexible body had major benefits – but scientists and engineers have had trouble nailing down the principles that govern its usefulness, and how to take advantage of them.

“Our thought was, well, animals solved this problem long, long ago,” Costello said. “Why don’t we look empirically at the flexible structures … and see if we find any kind of unifying pattern for their design?”

Costello and his colleagues looked to the animal kingdom to see if they could find some common features in a diverse set of flexible body plans. They culled 112 clips from sites like YouTube and Vimeo depicting 59 different species of flying and swimming animals in action, including moths, bats, birds and even humpback whales. They wanted to see where exactly the animals’ wings (or fins) bent most, and exactly how much they bent. They only used videos where the animals were flying directly toward or away from the camera, and videos with enough flapping time that they could see a regular pattern.

To their surprise, the scientists found a remarkable level of similarity among most of these species. Their flapping appendages on average bent about 65% of the way down the limb’s length, and the average bending angle was 26.5 degrees. The range of variation was pretty narrow too: Their major bending spots were anywhere from just 56% to 74% down the limb, and, the bending angle range was 14.5 to 38.4 degrees. Whether you were a feathered flier or a smooth-skinned manta ray, these animals tended to bend in the same way.

Size did not seem to affect these rules, Costello said. Nor did whether the medium was water or air. Even relatedness among species appeared to have a very tiny effect within these general principles.

“The actual way they bent and moved, the fact that there were such similarities between groups was really surprising to us,” Costello said.

The findings should give scientists and engineers some very helpful guidelines for building flexible robots that save energy and last longer – potentially very important for long-distance travelers.